On the black solid draw an ellipse mask, doesn't have to be perfect, you can free hand it, in fact it sells it better if it isn't perfect. Add the effect "Roughen Edges" to the solid layer. Adjust your settings to either get a real soft or extremely detailed edge. After you have that, keyframe your mask expansion until the mask is completely off the screen (this is why you need the larger layer size). Then set your Layer 2's track matte to alpha inverted and there you go. All in after effect ink reveal effect